Celery Black Streak Disorder Is Promoted by High Temperatures

Since 2005, a new physiological disorder known as ‘black streak’ has affected celery (Apium graveolens) quality in Michigan. Plants displaying black streak appear to be healthy; however, when trimmed, sporadic petioles will display black streaks that either extend throughout the entire petiole, or are dispersed irregularly within the petiole.  This defect makes the entire crop unmarketable, resulting in significant losses to growers.  The incidence of the problem has generally been high following hot weather, suggesting that high air temperatures may be implicated in its occurrence.  Therefore, this study was conducted to test the impact of temperature on the occurence of black streak in celery under field conditions.  The celery cultivar Dutchess (the most succeptible cultivar) was used for the studies in 2010 and 2011.  Treatements included no heat stress, and heat stress imposed at 5, 6, 7, 8, 9, and 10 weeks after transplanting (WAT).  Heat stress was created by covering the entire bed with perforated polyethylene row covers supported by hoops.  The heat stress was maintained for one week after which the row covers were removed.  Temperature and humidity sensors were placed within each treatment to monitor climatic conditions.  At havest, the celery was assessed for the presence of black steak symptoms in the petioles.  The row covers succesfully increased maximum air temperature above 90 °F in all years.  The number of plants and petioles affected by black streak was significantly higher in treatments that received heat stress.  This is a clear indication that hot temperature are implicated either directly or indirectly in the occurrence of black streak in celery. Incidence of the disorder varied with celery growth stage.  Symptoms increased with time, reached a maximum and then declined.  Maximum incidence was at 9 and 8 WAT in 2010 and 2011, respectively.  These results suggest that the growth stage when high temperatures occur is as important as temperature for development of black streak. Identifying environmental conditions that promote the occurrence of back streak in celery is only the first step in understanding this disorder.  Current management recommedation is to avoid growing susceptible cultivars during the hottest period of the season.